OAKLAND -- Pitcher Matt Harrison could return to the Rangers' rotation as early as Friday against the Mariners.

Harrison threw a light bullpen session on Monday and is expected to throw a longer one on Tuesday. If that goes well, Harrison could start on Friday against the Mariners.

"We'll make a determination after he gets all his work in," manager Ron Washington said.

Harrison put himself in position to return with eight scoreless innings on Saturday in his third medical rehab start for Double-A Frisco. Harrison went into the game determined not only to get his work in and get his pitch-count up, but also to get better results than his two previous outings. He appeared to have succeeded in achieving his goal and not worrying about outside distractions like how much longer he would need before he got back to the big leagues.

"Before the innings started, I started thinking about that stuff and squashed it," Harrison said. "I went out there and was focused on each pitch and staying on the attack. It's amazing how your goals and focus can dictate the outcome of the game."

Harrison won 18 games for the Rangers in 2012 and was their Opening Day pitcher in 2013. But he was shut down after two starts because of a herniated disc in his lower back. He twice underwent surgery on April 23 and May 1 and did not return the rest of the year. He had an additional surgery on Sept. 9 on his right non-throwing shoulder to alleviate Thoracic Outlet Syndrome.